As demands for a display have been recently expanded to a large-area and high-resolution TV, a 3D TV, an autostereoscopic TV, a large AMOLED, a high-resolution table PC, and the like, a high characteristic for a thin film transistor (hereinafter, referred to as a “TFT”) that is a driving element has been demanded.
It is necessary to stably manufacture the element in a large-area and high-resolution display in response to demands for competitive price, and such a demand induces people to have interests in an oxide TFT having an oxide semiconductor as an active layer, rather than an a-Si TFT or a low temperature poly silicon (LPTS) TFT based on Si. Development of the oxide TFT has greatly advanced in the last 5 to 8 years, so that a UD-level 3D TV with 70 inches was developed in 2011. An AMOLED having 55 inches driven with the oxide TFT was produced in 2012.
One of the most important factors for manufacturing a large-area and large-resolution display is an oxide TFT with high mobility. The mobility of the oxide TFT is closely related to a quantity of carriers inside a semiconductor. The mobility of the oxide TFT tends to be increased as the quantity of carriers is increased. However, since the increase of the quantity of carriers induces negative shift of a threshold voltage Vth, as well as the increase of the mobility, there is a technical limit in obtaining the oxide TFT having a high mobility characteristic. Especially, oxygen deficiency Vo and hydrogen inflow into the semiconductor are widely known as main factors of generating the carriers inside the oxide semiconductor. Accordingly, it is very important to manufacture an element so that the oxide TFT may be stably behaved without being influenced by hydrogen, and the like, until a final time point at which the display, such as a TFT-LCD or an AMOLED, is completely manufactured. The oxide TFT is sensitive to moisture, and the like, so that a protection layer is required, and in this case, a most widely used thin film is SiNx. However, since hydrogen inflow has been already generated in a process of depositing SiNx, the threshold voltage Vth of the oxide TFT is negatively shifted. Especially, since the oxide TFT having high mobility is in a state in which the quantity of carriers within the semiconductor is already increased in order to make a high mobility state, an element characteristic may sensitively react by inflow of a small quantity of hydrogen, and thus uniformity of an entire panel deteriorates, thereby decreasing a yield. Accordingly, a technology capable of preventing hydrogen inflow when forming the protection layer of the oxide TFT with high mobility is highly required.
In the meantime, when the AMOLED is manufactured, an OLED itself is sensitive to moisture, so that a protection layer for passivating the OLED is formed. In this case, even though the OLED is formed in a top emission type or a bottom emission type after an oxide TFT array is formed, a part of the oxide TFT may be exposed to the passivation process of the OLED, so that an oxide TFT stable even in a process of forming the protection layer of the OLED is demanded.